Chapter 6: Toxic Metals and Elements

sources of toxic metals

• naturally occurring deposits

• smelters

• coal-fired power plants

• factories

• hazardous waste sites

• contaminated food and water

Agency for Toxic Substances and Disease Registry (ATSDR)

created following CERCLA in 1980, it has identified a list of rank-ordered hazardous substances, known as the CERCLE Priority List of Hazardous Substances

CERCLA Priority List of Hazardous Substances

• created by ATSDR

• revised and published on a 2 year basis with a yearly review and revision

• includes substances with either the most significant threat to human health or substances with low toxicity but high frequency of occurrence and exposure

National Priorities List (NPL)

• EPA’s list of the most serious uncontrolled or abandoned hazardous waste sites in the US identified for possible long-term remedial action under Superfund

• sites scores based on Hazard Ranking System, updated yearly

NPL by February 2020

• 1335 superfund sites

• 51 proposed NPL sites

• 424 deleted NPL sites

What are the Superfund Sites in Bloomington?

Bennett Stone Quarry, Lemon Lane Landfill, and Neal’s Landfill

polychlorinated biphenyls (PCBs)

chemically stable, environmental persistent, lipophilic, with extended application in industry (plastic, resins, carbonless copy paper); even after being banned from industry, 1 million tons have been produced and 70% are still in use

Health Effects of PCBs

• studies have shown that they accumulate in human tissues, breast milk, and reproductive organs

• group 2A carcinogenic or probably carcinogenic

• endocrine disruptors associated with endometrial cancer and thyroid cancer

Metal Cycles

• present in lithosphere

• mobilized by weathering

• transported by water and wind

• absorbed by organisms

• end up in ocean sediment or agricultural land

• become more concentrated and harmful as they move up the food chain

Acute Metal Exposure

rapid onset, from a few minutes to one hour; may consist of gastrointestinal effects and neurological effects depending on mode of entry

Chronic Metal Exposure

• difficult to differentiate from chronic medical conditions, requires long-term exposure

• reduced cognitive function, cardiovascular disease, cancer

Gender Differences

• women have a higher prevalence of nickel-induced allergy and eczema

• cadmium retention is higher in women than men; Itai-Itai disease is mainly found in women; cadmium also has estrogenic effects impacting offspring

• differences attributed to hormonal and metabolic processes, women also smaller than men

Fetal Exposure to Heavy Metals

• lead and mercury can cross the placental barrier

• when exposure occurs during pregnancy, damage can cause fetal brain impairment

Lead Production

• mined as sulfide PbS

• sintered and roasted

• world production is 3 million tons per year

• 70% of US consumption is for batteries, but is also used for ammunition, cables, glass TV tubes, and solder

Sources of Lead

• until 1980s, leaded gasoline was primary source

• burning contaminated oil

• smelting ores

• incineration

Lead in Humans

directly absorbed, distributed, and excreted

1990s Lead Toxicity

11% of US urban children were affected, 22% African American and 13% Mexican American

What is the current blood lead reference value for children and pregnant women?

3.5 mcg/dL

Flint Disaster

• 2013-2019

• 99,000 households exposed to high levels of lead

• water source switched from Lake Huron to polluted Flint River

• 3% of tested children had BLLs greater than 5 mcg/dL

blood lead testing

in the US, there is routine blood lead testing for children living below the poverty levels as well as children enrolled in Medicaid

Household Lead Exposure

• drinking water from lead pipes

• house paint (until 1970s

• children and malnourished children vulnerable

Occupational Lead Exposure

• bridge maintenance

• battery manufacturing

• shipbuilding

• radiator repair

• smelter and foundry operation

• inhaling fumes from ammunition

How does lead damage the human body?

• it can mimic and inhibit the role of calcium and zinc

• distributed to blood, soft tissue (kidney, bone marrow, liver, and brain), and mineralized tissue (bones and teeth)

Calcium and Cell Function

• in the cell, it plays a role in signaling pathways, secondary messaging for release of neurotransmitters, muscle contraction, and as a cofactor

• outside of the cell, it maintains the possible differentiation across excitable cell membranes and aids in bone formation

Health Effects of Lead

• anemia

• dullness, irritability

• headaches, memory loss

• muscle tremors, loss of coordination

• hypertension

• nephrotoxicity in kidneys

• increased incidence of autoimmune disease

• affects cognitive development

Lead Risk Factors for Children

• increased GI absorption

• hand-to-mouth activity

• higher dust exposure

• incomplete development of blood-brain barrier

• peeling lead-based paint

Sources of Cadmium

• electroplating

• batteries

• pigments

• plastic stabilizers

• coal burning

• oil burning

• smelting

• waste incineration

Cadmium Transport

• in the air through fly ash, dry deposition, and wash-out

• in the water through soluble salts, organic complexes, and sediment

• in food as it is taken up by plants and bioaccumulated into food products

What is the target organ of Cadmium?

the kidneys

Cadmium Health Effects

• proteinuria and hypertension in the kidneys

• emphysema and cancer in the lungs

• osteoporosis in the bones

• Itai-Itai disease

• cardiovascular disease

• prostate cancer

• genotoxicity

• reproductive toxicity

• reduced life expectancy

Arsenic

• ubiquitous in nature

• varies in toxicity based on chemical form

• commercial applications as pesticide and wood preservative

• exposure through water and food

Inorganic Compounds of Arsenic

• present in water, treated woods

• more toxic and associated with cancer

Organic Compounds of Arsenic

• present in fish and shellfish

• less toxic

Where is arsenic high?

• Taiwan, Mexico, Chile, Argentina, Bangladesh, Mongolia

• New Mexico, Nevada, Utah, SoCal, Idaho, Nebraska

How does arsenic cause damage?

• inhibits essential metabolic enzymes so that cell energy source is disrupted promoting apoptosis

• inactivates NOs, reducing production of NO affecting vascular tone

Acute Arsenic Exposure

• vomiting

• abdominal pain

• diarrhea

• dehydration

• multisystem organ failure

• shock

• death

Chronic Arsenic Exposure

• caused by drinking contaminated water

• melanosis

• skin, bladder, kidney cancer

• lung cancer when inhaled

• associated with peripheral cerebrovascular disease, hypertension, diabetes, spontaneous abortion, stillbirths, preterm birth

Sources of Mercury

• coal combustion

• mining and smelting

• incineration of wastes

• medical waste incinerators

• textile manufacturing

• latex paints

• seafood

Mercury Target Organs

liver, kidneys, and lungs

Acute Mercury Poisoning

• symptoms begin with cough, chest tightness, trouble breathing, upset stomach

• pneumonia can develop

Organic Mercury

• methylated by bacteria in sediment, mollusks, fish

• bioaccumulates

• more toxic than inorganic, extremely soluble, can penetrate living membranes

• high affinity for sulfhydryl groups of catalytic sites, inactivating enzymes

• binds other proteins

• neurotoxin

• enters body through food ingestion, efficient GI absorption

• targets brain and cardiovascular system

Chronic Mercury Poisoning

• gingivitis

• mood and mental changes (CNS)

• nerve damage (PNS)

• intellectual disability, poor coordination, involuntary movement, and salivation in infants

Essential Metals

copper, zinc, and iron

Health Effects of Excess Copper

irritation of respiratory tract and gastrointestinal symptoms, liver and renal damage

Health Effects of Excess Zinc

stomach cramps, nausea, vomiting

Health Effects of Excess Iron

affects intestinal tract, liver, CNS, low blood pressure

Hemochromatosis

hereditary tendency of increasing iron absorption from food

Nanoparticles

man-made particles less than 100 nanometers, made from carbon and various metals

Nanoparticle Use

• anti-cancer therapies

• drug delivery

• cosmetics, sunscreen

• nano silver as antibacterial

Health Effects of Nanoparticles

• industrial approach is new, so effect on human health and environment is unknown

• easy to penetrate lungs and beyond

• they have the potential to harm human health